Generating a top-down mapping

In the top-down mapping approach, you generate a default database schema and mapping based on one or more existing enterprise beans. The enterprise beans is required to be at either EJB 1.1, 2.0, or 2.1 specification-level. The EJB to RDB mapping tools do not support using enterprise beans at EJB 3.0 specification-level.

About this task

To generate a schema and map from existing enterprise beans using the top-down mapping approach:

Procedure

  1. In the Enterprise Explorer view of the Java™ EE perspective, select any of the following options:
    • EJB project
    • Deployment Descriptor identified with an EJB JAR icon This is an image of the EJB JAR icon.
  2. Right-click and then select Java EE > EJB to RDB Mapping (1.x-2.x) > Generate Map.
    Restriction: To use the EJB to RDB mapping wizard, you must close any of the following editors that might be opened for a particular EJB project:
    • EJB Deployment Descriptor for editing the ejb-jar.xml file
    • Mapping for editing the Map.mapxmi file
    • Physical Data Model (also known as SQL Model editor) for editing the databaseName.dbm file
  3. For EJB 2.x projects, select whether to Create a new backend folder or to Use an existing backend folder. If you choose to use an existing backend, and if you have previously generated a mapping, you must choose one of the following options:
    • Create and map unmapped elements: use this option if you have changed the backend or to the enterprise beans and want to create the new elements and update the map accordingly.
    • Open mapping editor on selected backend map: use this option to open the mapping editor, where you can make manual updates to the mapping.
    Click Finish to perform the action and exit the wizard.
  4. If you choose to create a new backend folder, click Next to continue creating your initial top-down mapping.
  5. Select Top-Down, and click Next.
  6. Select a Target Database.
  7. Type the Database name and Schema name.
  8. Optional: You can select one or both of the following check boxes:
    • Generate DDL
    • Add a column for collision detection: Use this option for EJB 2.x CMP beans to add a column to your relational table. This column is reserved to determine if a record has been updated. For more information about this collision detection column, refer to the related topic about adding a column for collision detection.
  9. Click Finish to create the top-down mapping, or click Next to further define inheritance.
  10. If inheritance exists, select additional enterprise beans from the list to add a leaf table for each checked bean that joins with the parent table, then click Finish.

Results

The EJB mapping tools create tables, columns, and constraints relating to a CMP bean and its fields, as well as a map of each CMP field to a column. You can then make any required changes to these maps using the Mapping editor. Use the relational database tools to modify the tables and columns.
Related tasks:
Adding a column for collision detection when generating a top-down mapping
Feedback